High-resolution electron microscopy and X-ray diffraction study of intergrowth structures in α- and β-type YbAlB4 single crystals

Structural features of layered boride YbAlB₄ single crystals with YCrB₄-type (α-type) and ThMoB₄-type (β-type) phases derived from a hexagonal AlB₂-type structure were investigated by electron diffraction, high-resolution electron microscopy and X-ray diffraction. X-ray diffraction experiments indicate the existence of some structural motifs. High-resolution images clearly show that the structural motifs build the intergrown lamellar structures in the matrix. The lamellar structures can be characterized by a coherent tiling of deformed Yb hexagons, which are a common structure unit in the α- and β-type structures. The characteristic intergrown nanostructure is similar to that observed in the β-type TmAlB₄ polycrystalline sample.     

Charge ordering modulations in a Bi0.4Ca0.6MnO3 film with a thickness of 110 nm

The low temperature sample stage in a transmission electron microscope is used to investigate the charge ordering behaviours in a Bi0.4Ca0.6MnO3 film with a thickness of 110 nm at 103 K. Six different types of superlattice structures are observed using the selected-area electron diffraction （SAED） technique, while three of them match well with the modulation stripes in high-resolution transmission electron microscopy （HRTEM） images. It is found that the modulation periodicity and direction are completely different in the region close to the Bi0.4Ca0.6MnO3/SrTiO3 interface from those in the region a little further from the Bi0.4Ca0.6MnO3/SrTiO3 interface, and the possible reasons for this are discussed. Based on the experimental results, structural models are proposed for these localized modulated structures.     

Charge ordering modulations in Bi0.4Ca0.6MnO3 film with a thickness of 110 nm

Low temperature sample stage in transmission electron microscope is used to investigate the charge ordering behaviours in Bi_0.4Ca_0.6MnO₃ film with a thickness of 110 nm at 103 K. Six different types of superlattice structures are observed using selected-area electron diffraction (SAED) technique, while three of them match well with the modulation stripes in high-resolution transmission electron microscopy (HRTEM) images. It is found that the modulation periodicity and direction are completely different in the region close to the Bi_0.4Ca_0.6MnO₃/SrTiO₃ interface from those in the region a little far from the Bi_0.4Ca_0.6MnO₃/SrTiO₃ interface, and the possible reasons are discussed. Based on the experimental results, structural models are proposed for these localized modulated structures.     

Charge ordering modulations in a Bi_0.4Ca_0.6MnO₃ film with a thickness of 110 nm

The low temperature sample stage in a transmission electron microscope is used to investigate the charge ordering behaviours in a Bi 0.4 Ca 0.6 MnO 3 film with a thickness of 110 nm at 103 K.Six different types of superlattice structures are observed using the selected-area electron diffraction(SAED) technique,while three of them match well with the modulation stripes in high-resolution transmission electron microscopy(HRTEM) images.It is found that the modulation periodicity and direction are completely different in the region close to the Bi 0.4 Ca 0.6 MnO 3 /SrTiO 3 interface from those in the region a little further from the Bi 0.4 Ca 0.6 MnO 3 /SrTiO 3 interface,and the possible reasons for this are discussed.Based on the experimental results,structural models are proposed for these localized modulated structures.     

Diamond-like amorphous carbon and nanocrystalline diamond obtained by detonation method

Abstract

The diamond-like amorphous carbon phase was obtained by means of detonation compression of mixtures of an explosive with soot or graphite. The pycnometric density of powders after compression and treatment in boiling acids achieved 3.42 g/cm³. The X-ray and TEM study showed that fine-grained crystalline and nanocrystalline diamond was also present in the samples in addition to the diamond-like amorphous phase.     

石墨烯的透射电子显微学研究

石墨烯（Graphene）是近几年迅速发展起来的研究热点材料之一.利用透射电子显微镜（TEM）研究Graphene的结构特征和原子动态过程,是 Graphene研究的重要进展.文章评述了利用透射电子衍射方法对Graphene的层数、堆垛方式、取向和表面形貌等结构特征进行的研究工作,介绍了利用高分辨透射电子显微术在Graphene的表面缺陷、边缘结构及吸附原子等研究领域取得的最新结果.     

Phase transitions induced by shock compression on a gypsum mineral: X-ray and micro-Raman analysis

As a part of systematic researches of phase transitions induced by shock compression in phosphates, silicates, germanates and sulfates, in this article we report preliminary results obtained from shock recovery experiments on powders of a gypsum mineral. The shock experiment was performed in a light gas gun until a pressure close to 14?GPa reached. The experimental techniques employed to analyze the shock effects on recovered samples were: Scanning Electron Microscopy (SEM), X-ray Powder Diffraction (XRD) and Micro-Raman Spectroscopy (MRS). The SEM observations show a high plasticity in the impacted sample composed mainly by gypsum and bassanite quantified by Rietveld analysis of the XRD. The results indicate the partial dehydration of gypsum as a result of impact. The MRS analysis suggests the presence of micro-mixtures of gypsum, bassanite and anhydrite heterogeneously distributed throughout the recovered sample.     

测定微小晶体结构的电子晶体学图像处理技术

介绍了2005年国家自然科学奖二等奖获奖项目“微小晶体结构测定的电子晶体学研究”，研究目的是建立一种借助高分辨电子显微像测定晶体结构的新方法．为此提出了高分辨电子显微学与衍射晶体学相结合的思想，在实现此思想的过程中，研究了像衬的规律，得出实用的像衬公式和理论，阐明了不同种类原子像衬与晶体厚度的关系，而且用理论指导实验，观察到晶体中锂原子的像衬，以此理论为依据，把衍射晶体学中的多种分析方法特包是直接法引入到高分辨电子显微学中，建立了一套全新的电子晶体学图像处理技术，开发了相应的可视化专用软件包，并应用于测定多个未知晶体结构．文中逐一介绍了研究工作全过程的关键问题和研究结果。     

测定微小晶体结构的电子晶体学图像处理技术

介绍了2005年国家自然科学奖二等奖获奖项目“微小晶体结构测定的电子晶体学研究”.研究目的是建立一种借助高分辨电子显微像测定晶体结构的新方法.为此提出了高分辨电子显微学与衍射晶体学相结合的思想,在实现此思想的过程中,研究了像衬的规律,得出实用的像衬公式和理论,阐明了不同种类原子像衬与晶体厚度的关系,而且用理论指导实验,观察到晶体中锂原子的像衬.以此理论为依据,把衍射晶体学中的多种分析方法特包是直接法引入到高分辨电子显微学中,建立了一套全新的电子晶体学图像处理技术,开发了相应的可视化专用软件包,并应用于测定多个未知晶体结构.文中逐一介绍了研究工作全过程的关键问题和研究结果.     

钒的高压声速测量

采用反向碰撞方法进行了钒冲击实验,利用激光干涉测速技术对V/LiF窗口界面粒子速度剖面进行测量.通过对粒子速度剖面的分析获得了32—88 GPa压力范围内钒的高压声速.实验获得的声速-冲击压力关系在约60 GPa存在间断,表明钒发生了冲击相变.相变压力与静高压实验结果及第一性原理计算结果基本一致.     

Synthesis of CsCl-type single-phase RuSi under shock compression

Shock recovery experiments were performed on ruthenium–silicon powder mixtures by a flyer plate impact technique. The flyer velocities were in the range of 0.46–2.73 km/s, and the incident shock pressures were calculated to be ～2.9–～40.4 GPa by the impedance matching method. The recovered samples were characterized by X-ray diffraction and scanning electron microscopy. Results indicate that shock could induce a reaction between ruthenium and silicon. The shock pressure was found to affect reaction kinetics and microstructure of the recovered sample significantly. The dynamic reaction has a threshold pressure, and the samples loaded above threshold pressure almost completely reacted to a single-phase intermetallic compound of CsCl-type RuSi. These results indicate that shock compression could be an effective way to synthesize RuSi.     

冲击压缩下金属钯的结构相变

钯作为典型高压标定材料,研究其在极端条件下的结构变化以及热力学性质具有广泛需求并充满了挑战,特别是冲击加载下钯的固-固相变过程研究仍然匮乏.本文基于嵌入原子势,使用经典分子动力学方法从原子角度揭示了冲击载荷加载下钯的结构相变路径,在0—375 GPa的压力区间观察到一系列复杂的结构转变特征,从初始的面心立方(FCC)结构,至带密排六方(HCP)结构的层错体心立方(BCC)结构,直至完全熔化.在沿<100>晶向冲击下,在70.0 GPa发现了FCC-BCC相变过程,远低于之前研究中静高压的结果.此外,还发现了冲击方向依赖的相变点,在沿着<110>及<111>晶向冲击时FCC-BCC相变压力分别增加至135.8和165.4 GPa,同时相比完美晶体,引入缺陷会使FCC-BCC相变压强值有20—30 GPa的增幅,并通过势能分布的分析予以验证.本文发现冲击加载下钯的FCC-BCC相变压力大大降低的特殊现象,为钯在高压实验等极端条件下的应用提供了新的理论认识.     

自由电子气模型计算金属材料冲击压缩极限压缩度

用简单的自由电子气模型对金属铁、铜、铝、铅的冲击压缩特性进行了数值计算,计算结果表明材料并不能无限地被压缩,存在极限压缩度,随着压缩度的增加,在冲击压力增加的同时,冲击温度也急剧上升,限制了材料的进一步压缩,本文计算的这几种材料的极限压缩度为3.9.     

多次冲击波压缩DT冰理论研究

冲击波压缩DT是ICF内爆过程中的主要熵增因素,如何用有限数目的时间整形冲击波实现近等熵压缩过程是优化点火靶设计的关键。利用理想气体和实际DT状态方程,计算系列冲击波压缩后的熵增和密度变化,分析表明,当第一个冲击波压强不大于0.1 TPa,后续再用3个冲击波达到10 TPa,总熵增不影响点火靶DT压缩性能,增加冲击波个数对DT熵增和压缩度改善效果很小。     

Microstructure and photocatalytic activity of titanium dioxide nanoparticles

Titanium dioxide nanoparticles with an average diameter of about 10 nm are fabricated using a sintering method. The degradation of methyl orange indicates that the photocatalytic efficiency is greatly enhanced, which is measured to be 62.81%. Transmission electron microscopy is used to investigate the microstructure of TiO 2 nanoparticles in order to correlate their photocatalytic properties. High-resolution transmission electron microscopy examinations show that all the nanoparticles belong to the anatase phase, and pure edge dislocations exist in some nanoparticles. The great enhancement of photocatalytic efficiency is attributed to two factors, the quantum size effect and the surface defects in the nanoparticles.     

Ultramicrotomy reveals crystallographic information on a sectioned surface of a metallic block specimen

Ultramicrotomy is widely regarded as a thin section preparation method for transmission electron microscopy (TEM) investigations. It is shown that ultramicrotomy can also provide a simple path for microstructure analysis and assessment of mechanical properties for a sectioned block-face. Furthermore, electron backscatter diffraction (EBSD) analysis can be applied directly on ultramicrotomed surfaces without any additional polishing or etching. EBSD analysis relates the inherent cutting artefacts to the crystallographic orientations of the grains, hence delivering a rough assessment of their deformation resistance. TEM investigations revealed that crystallographic-related cutting artefacts, which exhibit a wave-like pattern, are the result of the dislocation pile-ups close to the knife–specimen interface. This technique is considered suitable to be coupled with EBSD for three-dimensional microstructure reconstructions when used for serial sectioning of large volumes.     

Experimental verification of Foreman dislocation model

We present a strain analysis of an edge dislocation core, and a detailed discussion of the Foreman dislocation model. In order to examine the model, the quantitative measurement of strain field around an edge dislocation in aluminum is performed, and high-resolution transmission electron microscopy and geometric phase analysis are employed to map the strain field of the edge dislocation core in aluminum. The strain measurements are compared with the Foreman dislocation model, showing that they are in good agreement with each other when 0.7 ≤ a ≤ 1.5.